Remove unused variable.

Python/bltinmodule.c

@@ -37,7 +37,7 @@ builtin___build_class__(PyObject *self, PyObject *args, PyObject *kwds)
 {
     PyObject *func, *name, *bases, *mkw, *meta, *winner, *prep, *ns, *cell;
     PyObject *cls = NULL;
-    Py_ssize_t nargs, nbases;
+    Py_ssize_t nargs;
     int isclass;
 
     assert(args != NULL);
@@ -62,7 +62,6 @@ builtin___build_class__(PyObject *self, PyObject *args, PyObject *kwds)
     bases = PyTuple_GetSlice(args, 2, nargs);
     if (bases == NULL)
         return NULL;
-    nbases = nargs - 2;
 
     if (kwds == NULL) {
         meta = NULL;